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Date: Wed, 12 Feb 2020 15:56:46 -0500
From: Rich Felker <dalias@...c.org>
To: "A. Wilcox" <awilfox@...lielinux.org>
Cc: musl@...ts.openwall.com
Subject: Re: bug#39236: coreutils cp mishandles error return from
 lchmod

On Wed, Feb 12, 2020 at 01:59:09PM -0600, A. Wilcox wrote:
> On 12/02/2020 13:07, Rich Felker wrote:
> > On Wed, Feb 12, 2020 at 08:05:55AM -0500, Rich Felker wrote:
> >> On Wed, Feb 12, 2020 at 12:50:19PM +0100, Florian Weimer wrote:
> >>> * Paul Eggert:
> >>>
> >>>> On 1/22/20 2:05 PM, Rich Felker wrote:
> >>>>> I think we're approaching a consensus that glibc should fix this too,
> >>>>> so then it would just be gnulib matching the fix.
> >>>>
> >>>> I installed the attached patch to Gnulib in preparation for the upcoming 
> >>>> glibc fix. The patch causes fchmodat with AT_SYMLINK_NOFOLLOW to work on 
> >>>> non-symlinks, and similarly for lchmod on non-symlinks. The idea is to 
> >>>> avoid this sort of problem in the future, and to let Coreutils etc. work 
> >>>> on older platforms as if glibc 2.32 (or whatever) is already in place.
> >>>
> >>> The lchmod implementation based on /proc tickles an XFS bug:
> >>>
> >>>   <https://sourceware.org/ml/libc-alpha/2020-02/msg00467.html>
> >>
> >> Uhg, why does Linux even let the fs driver see whether the chmod is
> >> being performed via a filename, O_PATH fd, or magic symlink in /proc?
> >> It should just be an operation on the inode.
> > 
> > OK, I don't think it's actually clear from the test that the use of
> > the magic symlink is the cause. It's plausible that XFS just always
> > returns failure on success for this operation, and I don't have XFS to
> > test with.
> 
> 
> My root fs is XFS, but I only have musl to test with.  Is there a test
> case I can run on musl to determine the behaviour of XFS for you?
> 
> The only glibc distribution that supports my platform is Void, so I
> don't know if the Void glibc spin in a chroot would be sufficient if
> there is no way to do this from a musl system.

We've since found (in the other thread musl list isn't CC'd on) that
this does not seem to be XFS-specific but happens in ext4 too, and is
probably a high level vfs bug.

Rich

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